This application is based on Japanese patent application, No. JPAP2000-345959 filed on Nov. 13, 2000, in the Japanese Patent Office, the entire contents of which are incorporated by reference herein.
1. Field of the Invention
This invention relates generally to a method and apparatus for image forming. More particularly, the invention relates to effectively transferring various kinds of powder.
2. Discussion of the Background
Many image forming apparatuses such as copying machines, facsimile machines, printers, and multi-function apparatus combining features of these machines use a powder pump for transferring toner in a powder form or a two-component development agent including toner and carriers. A powder pump, which is used in image forming apparatuses, generally includes a stator having a through-hole formed with two grooves extended in a stator spiral form and a rotor configured for free rotation inside the through-hole of the stator. The rotor extends in a rotor spiral form such that spaces for accommodating a powder are formed between an outer circumferential surface of the rotor and an inner circumferential surface of the through-hole of the stator. The rotor is configured to rotate, moves the spaces, and thereby transfers the powder. One example of this type of the powder pump that is known as a single-shaft eccentric screw pump or a mono pump is described in published Japanese patent application, No. 11-84873.
A single-shaft eccentric screw pump or a mono pump is configured such that the spaces formed between the outer circumferential surface of the rotor and the inner circumferential surface of the through-hole of the stator are moved by the rotation of the rotor and consequently the powder sealed inside the spaces are transferred. Generally, the rotor is made of a rigid material such as metal or resin. The stator is made of an elastic material such as a rubber.
The inventors of the present invention realized that to configure the powder pump capable of transferring a maximum amount of the powder in a unit time, the above-described spaces should be sealed as perfectly as possible so that a suction pressure at a powder suction side of the powder pump is increased. The outer circumferential surface of the rigid rotor contacts under pressure the inner circumferential surface of the through-hole of the elastic stator so that the inner circumferential surface of the through-hole is elastically deformed. An amount of this deformation of the stator is referred to as an engagement amount. As described above, to increase the sealing of the spaces, the contact pressure between the outer circumferential surface of the rotor and the inner circumferential surface of the through-hole of the stator around the spaces may be increased as much as possible, such that the engagement amount of the stator may be increased as much as possible.
However, when the engagement amount of the stator is increased in an indiscriminate manner, a torque of the rotor is increased, and consequently a wearing of the stator by a friction between the rotor and the stator is accelerated. This causes a rapid increase of a temperature of the powder pump. If the powder which is transferred by the powder pump is adversely effected by the increase in heat, then the powder is not properly transferred. For example, if the powder is a toner or a two-component development agent including toner and carriers, the powder inevitably becomes prone to be coagulated under the influence of the increased temperature.
It is an object of the present invention to provide a method and apparatus for transferring powder. In one aspect of the invention a novel powder pump apparatus is described wherein the apparatus includes (1) a stator including a through-hole formed with two grooves extended in a stator spiral form; and (2) a rotor configured and arranged for free rotation inside the through-hole of the stator, the rotor extends in a rotor spiral form such that spaces for accommodating a powder are formed between an outer circumferential surface of the rotor and an inner circumferential surface of the through-hole of the stator, The rotor is configured to rotate so as to move the spaces and thereby transfer the powder.
When the rotor has a cross-sectional diameter of at least RA millimeters and an outer diameter of at least RB millimeters, and the through-hole of the stator has inner diameter of SN millimeters and a largest inner diameter of SX millimeters, the cross-sectional diameter RA, the outer diameter RB, the least inner diameter SN, and the largest inner diameter SX are defined to satisfy formulas of
RAxe2x88x92SNxe2x89xa70.45 
and
RBxe2x88x92(SN+SX)/2xe2x89xa70.45. 
In another aspect of the invention, the cross-sectional diameter RA, the outer diameter RB, the least inner diameter SN, and the largest inner diameter SX may be defined to satisfy formulas of
xe2x88x920.18xe2x89xa6RBxe2x88x92(SN+SX)/2xe2x88x92(RAxe2x88x92SN)xe2x89xa60.16. 
In an additional aspect of the invention, the cross-sectional diameter RA, the outer diameter RB, the least inner diameter SN, and the largest inner diameter SX may be defined to satisfy formulas of
RAxe2x88x92SNxe2x89xa70.4, 
RBxe2x88x92(SN+SX)/2xe2x89xa70.4, 
and
xe2x88x920.18xe2x89xa6RBxe2x88x92(SN+SX)/2xe2x88x92(RAxe2x88x92SN)xe2x89xa60.12. 
In an additional aspect of the invention, the cross-sectional diameter RA, the outer diameter RB, the least inner diameter SN, and the largest inner diameter SX may be defined to satisfy formulas of
RAxe2x88x92SNxe2x89xa70.5, 
RBxe2x88x92(SN+SX)/2xe2x89xa70.5, 
and
xe2x88x920.18xe2x89xa6RBxe2x88x92(SN+SX)/2xe2x88x92(RAxe2x88x92SN)xe2x89xa60.12. 
In another aspect of the invention, the cross-sectional diameter RA, the outer diameter RB, the least inner diameter SN, and the largest inner diameter SX may be defined to satisfy formulas of
RAxe2x88x92SNxe2x89xa60.9 
and
RBxe2x88x92(SN+SX)/2xe2x89xa60.9. 
In an additional aspect of the invention, the rotor may be made of a material of at least one of aluminum, polycarbonate, and a polyacetal resin.
The stator may be made of at least one of an ethylenepropylene rubber having a hardness of 50 degrees in accordance with a scale A of a Japanese Industrial Standard and a chloroprene rubber.
The rotor may be driven at a rotation speed from about 100 rpm to about 400 rpm.
In an additional aspect of the invention, the powder may be toner or a two-component development agent including toner and carriers.
In another aspect of the invention, a novel method of toner transferring is described wherein the method includes (1) forming a through-hole with two grooves extended in a stator spiral form in a stator; (2) arranging a rotor extending in a rotor spiral form such that spaces for accommodating a powder are formed between an outer circumferential surface of the rotor and an inner circumferential surface of the through-hole of the stator; and (3) rotating the rotor so that the spaces are moved to transfer the powder. When the rotor has a cross-sectional diameter RA millimeters and an outer diameter RB millimeters, and the through-hole of the stator has a least inner diameter SN millimeters and a largest inner diameter SX millimeters, the cross-sectional diameter RA, the outer diameter RB, the least inner diameter SN, and the largest inner diameter SX are defined to satisfy formulas of
RAxe2x88x92SNxe2x89xa70.45 
and
RBxe2x88x92(SN+SX)/2xe2x89xa70.45. 
In an additional aspect of the invention, a novel image forming apparatus is described wherein the apparatus includes (1) a powder pump having a stator and a rotor. The stator has a through-hole formed with two grooves extended in a stator spiral form; (2) a rotor configured to rotate inside the through-hole of the stator. The rotor extends in a rotor spiral form such that spaces for accommodating a powder are formed between an outer circumferential surface of the rotor and an inner circumferential surface of the through-hole of the stator. The rotor is configured to rotate so as to move the spaces and consequently to transfer the powder. When the rotor has a cross-sectional diameter RA millimeters and an outer diameter RB millimeters, and the through-hole of the stator has a least inner diameter SN millimeters and a largest inner diameter SX millimeters, the cross-sectional diameter RA, the outer diameter RB, the least inner diameter SN, and the largest inner diameter SX are defined to satisfy formulas of
RAxe2x88x92SNxe2x89xa70.45 
and
RBxe2x88x92(SN+SX)/2xe2x89xa70.45. 
Additional objects and advantages of the invention will be set forth in the following description, and in part will be evident from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out herein.